The gas separation membrane has been utilized in various processes, which are deemed industrially important, such as air separation, separation of carbon dioxide from a natural gas, separation of nitrogen or hydrocarbon and hydrogen in petrochemistry process and the like. The gas separation membrane achieves the necessary selectivity that allows for separation of a desired gas and high permeability.
However, a membrane generally shows so-called trade-off phenomenon with respect to the selectivity and the permeability. That is, the membrane having the high selectivity shows low permeability, while the membrane having the high permeability shows low selectivity (Moaddeb Maryam et al., J. Membrane Sci., 1997, 125, 144).
Although many researchers have investigated various new materials to develop the highly efficient gas separation membrane that overcomes such trade-off phenomenon, there has been no discovery of such membranes so far (Pratibha Pandey, R. S. Chauha, Progress in Polymer Science, Vol. 26, Issue 6, 2001, 857).
An asymmetric membrane, which has a minimal thickness capable of maintaining its mechanical strength, was developed to prepare such highly efficient membrane on the basis that the permeation rate of gas is inversely proportional to the thickness of the membrane (H. Strathmann, K. Knock, P. Amar and R. W. Baker. Desalination 16 (1975), p. 179). Thereafter, more improved asymmetric membranes were developed. Although the permeation rate was increased, such asymmetric membranes, however, were deficient in that they contain pinholes that cause much pressure loss and decrease of selectivity.
Further, there has been developed a method that increases the gas permeation due to the increase of the permeation area, wherein a hollow fiber membrane is made in a form of bundle and both ends thereof are fixed with a thermosetting resin, such as epoxy resin or a hot melt thermoplastic resin, to fabricate the membrane as a membrane module (Membrane Separations Technology, Principles and Applications, Elsevier, 1995, pp. 467-498). The module has the increased permeation rate, but has the lower separation selectivity. Thus, it is difficult to achieve the module having a lightweight and small size. Furthermore, the module is disadvantageous since the fed gas has to be purified in advance.